This invention relates to an external barrier means for composite structures, for instance for use in the juncture between filament wound laminates of a pressure vessel or the like.
Heretofore, barrier coats have been applied to the external surfaces of composite structures such as filament wound pressure vessels, rocket motor cases or the like, to retard moisture or other adverse environment penetration into the composite case. Extended exposures in high humidity and elevated temperature environments can considerably degrade the strength of unprotected composites.
However, existing techniques utilizing barrier coats do not provide protection at the termination of the barrier coat where the composite case is attached to fittings, such as polar bosses, or other fixed members. Other problem areas where existing techniques utilizing barrier coates are deficient include areas where laminate skirt portions of a pressure vessel join a cylindrical portion of the vessel; e.g. a juncture between first and second laminate portions comprising the skirt and cylinder of a rocket motor case.
In such instances as described above, the juncture is capable of separating due to flexing of the adjacent components, such as under pressurization of the vessel. The external barrier coats also separate at the junctures, leaving a gap which is prone to moisture penetration.
The present invention is directed to an external barrier means for composite structures such as pressure vessels, rocket motor cases, or the like, to solve the above problems relating to moisture or gaseous penetration into the composite case.
The barrier means of the present invention is disclosed herein for use in a gap between the composite and a non-yielding member, such as a polar boss, of a pressure vessel during pressurization. The invention also is shown for use at the juncture between a skirt portion and a cylinder portion of a pressure vessel, such as a rocket motor case. However, it is to be understood that the barrier means of the present invention is equally applicable for use at junctures of a wide variety of vessels or casings where the juncture is capable of separating to create a gap which is prone to moisture penetration.
In the exemplary embodiment of the invention, the barrier means includes a flexible barrier member, such as rubber or the like, disposed between first and second components of a composite structure at a juncture which is capable of separating. The barrier member is sealed, as by bonding, to the components to prevent moisture penetration around the flexible barrier member. The barrier member further is split from the exterior thereof partially therethrough to accommodate separation of the components at the juncture there between. An enlarged portion is formed at the base of the split in the barrier member to preclude any stress-riser affect at the base of the split, thereby preventing the split from increasing inwardly upon any such separation at the juncture.
Preferably, a film sheet, such as Teflon or the like, is folded onto itself and disposed in the split in the barrier member to prevent the split portions thereof from adhering to each other. The fold in the film sheet is disposed generally at the base of the split in the barrier member, and a resilient member, such as an O-ring, is disposed in the fold and sized to fit into the enlarged portion of the split in the barrier member to hold the film sheet in place.
Thus, it can be seen that a new and improved barrier means is provided for use in a juncture between yieldable components of a composite structure to retard moisture or gas penetration into the composite structure where existing techniques utilizing barrier coats are deficient.
Other objects, features and advantages of the invention will be apparent from the following detailed description taken in connection with the accompanying drawings.